1. Field of the Invention
This invention relates to an apparauts for illuminating an original for use in an original reading apparatus for reading an original placed on an original supporting table, and more particularly to a device for illuminating an original effective for an apparatus for dividing an original into a plurality of areas and reading them.
2. Related Background Art
The device for illuminating an original of an image reading apparatus has heretofore been constructed as shown in FIG. 5 of the accompanying drawings. Referring to FIG. 5 which is a figure depicted to illustrate the difference from the present invention, the device for illuminating an original comprises a halogen lamp 3 comprising a group of filaments 1 wound in parallelism to the reading line 2 of an origin 4, and a reflecting member 5. As examples of applications similar to this, there are known many ones such as Japanese Laid-Open Patent Application No. 60-254125 and Japanese Laid-Open Patent Application No. 56-78853.
On the other hand, among image reading apparatuses, there is an apparatus of the movable optical system type which divisionally scans and reads an original, for example, a reading apparatus described in Japanese Laid-Open Patent Application No. 55-137767.
Now, in a lamp of the type in which a filament is made to emit light, the light emission distribution in the radial direction of the filament is most uniform, and in the lengthwise direction (the direction of arrow X in FIG. 5) of the filament, the light emission intensity of the winding portion thereof is greatest and the light emission intensity of the other portions is somewhat small. That is, in the lengthwise direction of the filament, the light emission distribution is not uniform.
In the prior-art apparatus wherein such a filament is disposed parallel to the reading line, the light emission intensity particularly on the lengthwisely opposite end portions of the lamp is small and therefore, the Shading phenomenon could not be avoided.